1. Field of the Invention
The invention relates to an image generation technology of an image for display on a display apparatus that is installed in a vehicle.
2. Description of the Background Art
Conventionally, an image display system that is installed in a vehicle and that displays, on an in-vehicle display, images of surrounding area taken by on-vehicle cameras is known. A driver can view a surrounding area of a vehicle in almost real time by using this image display system.
In an example, the area outside of the front fender on the opposite side of a driver's seat becomes a blind area for a driver, and the driver hardly recognizes clearances between own vehicle and obstacles in the area. On the other hand, using the image display system, images of the area outside of the front fender are taken by on-vehicle cameras and are displayed on a vehicle-cabin display. This system helps a driver to recognize easily clearances between a vehicle body and obstacles in the area on the opposite side of the driver's seat in a case like when approaching to a roadside.
These days, a new image display system is proposed. The new system generates composite images which show a surrounding area of a vehicle using plural images taken by plural on-vehicle cameras that are installed at different locations on the vehicle, and which are displayed in a manner viewed from virtual viewpoints e.g. from just above of the vehicle.
In an example of the image display system that generates composite images viewed from a virtual viewpoint, composite images are generated using four images taken by four on-vehicle cameras installed respectively on a vehicle, at the front, at the left side, at the right side, and at the rear of the vehicle. If composite images are generated by the method where the four shot images are connected simply at the prescribed boundaries, the generated object images lack continuity in the boundary areas between two adjacent shot images. Thus, it is difficult to recognize the objects existing in the boundary areas or passing through the areas.
To solve this problem, overlapped areas made by the areas shot by two adjacent on-vehicle cameras are provided. As a new proposed method, the images taken by two adjacent on-vehicle cameras are blended at a prescribed proportion for generating a composite image in a boundary area. This method reduces discontinuity of object images appeared on object images in the boundary area of two shot images and makes it easier to recognize the objects existing in the boundary area.
Generally, plural on-vehicle cameras that are used for generating composite images implement exposure control respectively.
In the case where headlights of a vehicle are on e.g. at night time because of darkness of surrounding area of the vehicle, an on-vehicle camera installed at the front of the vehicle (hereinafter referred to as a front on-vehicle camera) implements exposure control based on the relatively bright area that is lightened by headlights. On the other hand, an on-vehicle camera installed at the side of the vehicle (hereinafter referred to as a side on-vehicle camera) implements exposure control based on a very dark area with no lighting. Thus, the exposure controls quite different between the side on-vehicle camera and the front on-vehicle camera are implemented. The side on-vehicle camera implements exposure control to make images much brighter compared to the front on-vehicle camera. Thus, brightness of one object image existing in the overlap area becomes quite different between images taken by the front on-vehicle camera and by the side on-vehicle camera.
Therefore, two images of one object quite different in brightness are blended when two shot images in overlap area corresponding to the images taken by the front on-vehicle camera and by the side on-vehicle camera are blended to generate a composite image in overlap area (boundary area of two shot images). As a result, defects (such as whiteout and color migration) of the composite image in the overlap area occur, and visibility level of an object image in the overlap area is extremely deteriorated.